The vulnerability is limited to Flash files edited by hand with a binary editor but is serious nonetheless.
The Flash application will not produce files that contain the vulnerability on its own, according to a separate security alert from Macromedia.
The vulnerability is dangerous because it affects Web browsers, which are trusted by firewalls to receive incoming traffic, and because it affects all versions of Flash used in the Internet Explorer and Netscape Navigator Web browsers running on both Windows and Unix, eEye said.
The flaw comes as the result of a problem in the data header of Flash files, which allows an attacker to supply more data to the file decoder than is expected and, in turn, can lead to code execution, eEye said.
Because the vulnerability is browser-based, it can be exploited in any situation in which a Web browser views a Flash file, such as on Web pages, in e-mail or newsgroups, eEye wrote.
Macromedia has released more information about the flaw and a new Flash player that addresses the problem at: www.macromedia.com/v1/handlers/index.cfm?ID=23293&Method=Full&TitlePSB02%2D09%20%2D%20Macromedia%20Flash%20Malformed%20Header%20Vulnerability%20Issue&Cache=False